David Moyes insists he is the right man to turn Manchester United around – though, as he seeks a much needed win at Sunderland, the manager may have to deal with the sizeable blow of being without Robin van Persie and Wayne Rooney due to injury.

With United failing to score from open play in 450 minutes of league football the pair's potential absence would add to Moyes's growing difficulties.

United are already eight points behind the Premier League leaders, Arsenal, in 12th place, following last week's 2-1 defeat by West Bromwich Albion at Old Trafford. Despite a start that also includes losses to Liverpool and Manchester City, Moyes remains confident that, with United being traditionally slow starters, they will soon pick up results.

This week Sir Alex Ferguson, the former manager who chose Moyes to replace him, gave the Scot further backing. Asked about this, Moyes said: "It's a good club – I'm sure they know they have picked the right man for the job. Sir Alex was part of that process as well."

Asked how much faith Moyes has in his players pulling their title defence around, he said: "I don't think it's a case of pulling it around. It's just us getting back on track and finding a bit of form. We had a disappointing result against West Brom, disappointing performance against Manchester City, so we'll do everything we can to put that right. It's not been as bad as many people have made it out to be.

"Obviously our league position isn't where we want to be but let's just wait and see where it ends up come the end of the season."

United have a tradition of starting slowly and Ferguson often stated that, if the club were still in contention at the turn of the year, they had a chance. "Yeah, that's right, because they've tended most years not to get off to a good start. If you look at their history – even on the back of some tours, it's not always been the best either," Moyes said. "So from that point of view and with the way the Premier League put the fixtures out it was always going to be a difficult start."

Rooney is awaiting a late test on an injured shin. The striker did not play in the 1-1 Champions League draw at Shakhtar Donetsk on Wednesday after which Moyes stated he was hopeful of him recovering and being available for Saturday's thetrip to Sunderland.

The manager said: "I'm not more sure or less sure [than then]. I've just not seen him yet this [Friday] morning since he came in. I think he's responding well to treatment, he's had a lot of treatment on his shin and I'm hopeful he'll be OK."

Asked if Van Persie was fit, after he was seen limping after the draw with Donetsk, the manager said: "I think so, he's got a bit of a sore toe so I've not seen him either; [it won't be] until this afternoon."

If Moyes is without one or both of Rooney and Van Persie, it would make his task more difficult as they have registered six of United's eight league goals and the manager is conscious the side have not scored from open play since the opening day of the season.

Although previous injuries to Van Persie and Rooney mean they have started only two of the club's six league games so far this season, Moyes does not think this should excuse why United have registered only from dead balls since the 4-1 win at Swansea City.

"No. I don't think that is it because I think we've got other really good players and it wouldn't be down just to those two to score goals," he said. "We've got other players who are capable of scoring goals. We have to make sure that when Wayne and Robin are not available to us that we do have people who can take up the mantle."

Moyes also confirmed he would assess whether to buy new players in the next transfer window. "I'll look at January but I wouldn't want people to have big expectations about what you would sign or do in January," he said. "I don't think January [has], in the main, been a really good month to sign really at the top. If you're in trouble near the bottom of the league you might if you're desperate for something, but I think where we'll be with Manchester United we'll be looking for the top."

Moyes added that his challenge is to find a balance between attacking football and solid defensive play. "For me that's how I'd define it," he said. "We definitely want to be aggressive and attack and look to score. But in the same breath feel that you are comfortable defensively as well. So there is a balance which has to come between defence and attack. It takes time but this is a team which knows it, so the players are aware of it as well."